Download Lecture 2: Bioenergetics

Bioenergetics:
Calculating Energy Values in
Food
Introduction
Energy is required by all animals to sustain
life
 Sources: food, natural productivity, body
stores (times of environmental stress or
feed deprivation)
 Lecture objectives: How much energy is
needed by aquatic organisms?, How does it
varies from terrestrials?, What are the
sources, how is energy partitioned for
various uses
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Lecture objectives
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How much energy is needed by aquatic
organisms?
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How it varies from terrestrials?
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What are the sources?
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How is energy partitioned for various uses?
Introduction
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Lavoisier first demonstrated that oxidation of
nutrients was some form of combustion (burning)
Rubner (1894) first demonstrated that
fundamental Laws of Thermodynamics also applied
to intact living animal systems
Organic matter  processes  CO2 + H2O +
energy (released)
Understanding energy transforms is only possible
when it is converted from one form to another
Introduction
Energetics is the study of energy
requirements and the flow of energy within
systems
 bioenergetics is the study of the balance
between energy intake in the form of food
and energy utilization by animals for lifesustaining processes
 processes?: tissue synthesis,
osmoregulation, digestion, respiration,
reproduction, locomotion, etc.
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Introduction
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the original energy source for food energy is the
sun (See…I knew what I was talking about for once!)
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energy from the sun is converted by
photosynthesis into the production of glucose
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glucose is the hydrocarbon source from which
plants synthesize other organic compounds such as
COH, protein, lipids
as previously mentioned, one must consider the
quality of these sources
Introduction
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Animals are not heat engines
They can’t use the multitude of sources of energy
we have (e.g., flywheels, falling objects, the tide,
etc.)
Must obtain their energy from chemical bonds of
complex molecules
How do they do it? In a nutshell, they oxidize
these bonds to lower energy states using oxygen
from the air
Trick: some bonds have more energy than others
Introduction
most aquaculture animals obtain their energy
from feeds
 As mentioned, some bonds have more energy
associated with them than others
 when you have many nutrients comprising a
feed, the energy level of that feed can vary
substantially
 availability of energy varies according to feed
ingredient and species
 growth is the endpoint of net energy
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Glycogen Molecule
major COH storage form of energy
Lipid Molecule
another major storage form
Introduction (cont.)
Energy goes through many cycles and
transformations, always with loss of heat
 can be released at various rates: gasoline
can exploding vs. compost pile
 nutritional energetics involves the study of
the sources and transformations of energy
into new products (mainly we are concerned
with growth or tissue deposition)
 of all dry matter we consume, 70-90% goes
to synthesis of new products
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Energy Forms
Matter and energy are basically the same
 it is often convenient to consider energy a
property of matter (kcal/g feed)
 nutritive value of food items is often
reflected by calories
 what you are used to seeing in the store is
not calories, but kilocalories (kcal’s), or
Calorie
 common form of energy in the cell is ATP
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Energy Forms
All processes in the animal body involve
changes in energy
 the word “energy” was first introduced in
1807, and defined as “ability to work”
 found in many forms: heat, kinetic,
electromagnetic, radiant, nuclear and
chemical
 for our purposes, chemical energy is the
most important (e.g., ATP)
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Heat Energy
The measurement of energy requires
converting it from one form to another
 what we typically measure is heat (why?)
 according to the first law of
thermodynamics, all forms of energy can
be converted quantitatively into heat
energy
 heat energy is represented by the various
constituents of the diet
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Heat Energy
 however,
the body is not a heat
engine, heat is an end product of
reactions
 it is only useful to animals to keep the
body warm
 chemical reactions either generate
heat (+H) or require heat (- H)
Units of Heat Energy
The basic unit of energy is the calorie (cal)
 it is the amount of heat required to raise
the temperature of 1g of water 1 degree
Celsius (measured from 14.5 to 15.5oC)
 it is such a small unit, that most
nutritionists prefer to use the kcal (or
1,000 calories)
 REM:the kcal is more common
(supermarket Calories)
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Other Units of Heat Energy
 BTU
(British Thermal Unit) = amount
of heat required to raise 1 lb of
water 1oF
 international unit: the joule - 1.0
joule = 0.239 calories or 1 calorie =
4.184 joule
 a joule (J) is the energy required to
accelerate a mass of 1kg at a speed
of 1m/sec a distance of 1m
Energy Terms (from De Silva
and Anderson)
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Energy flow is often shown as a diagram: every
text has its own idea of a suitable diagram:
Energy Terms
Gross energy (GE): energy released as
heat resulting from combustion (kcal/g)
 Intake Energy (IE): gross energy
consumed in food (COH, lipid, protein)
 Fecal Energy (FE): gross energy of feces
(undigested feed, metabolic products, gut
epithelial cells, digestive enzymes,
excretory products)
 Digestible Energy (DE): IE-FE
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Energy Terms (cont.)
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Metabolizable energy (ME): energy in the food minus
that lost in feces, urine and through gill excretion:
ME = IE - (FE + UE + ZE)
urinary energy (UE): total gross energy of urinary
products of unused ingested compounds and metabolic
products
gill excretion energy (ZE): gross energy of products
excreted through gills (lungs in mammalian
terrestrials), high in fish
surface energy (SE): energy lost to sloughing of mucus,
scales, exoskeleton
Energy Terms (cont.)
Total heat production (HE): energy lost in
the form of heat
 heat lost is sourced from metabolism, thus,
HE is an estimate of metabolic rate
 measured by temperature change
(calorimetry) or oxygen consumption rate
 divided into a number of constituents
 as per energy flow diagram 
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Energy Flow Diagram
Energy Terms
(total heat production)
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Basic metabolic rate (HeE): heat energy released from
cellular activity, respiration, blood circulation, etc.
heat of activity (HjE): heat produced by muscular
activity (locomotion, maintaining position in water)
heat of thermal regulation (HcE): heat produced to
maintain body temp (above zone of thermal neutrality)
heat of waste formation (HwE): heat associated with
production of waste products
specific dynamic action (HiE): increase in heat
production following consumption of feed (result of
metab), varies with energy content of food, especially
protein
Energy Utilization
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Energy intake is
divided among all
energy-requiring
processes
Magnitude of each
depends on quantity of
intake plus animal’s
ability to digest and
utilize that energy
Can vary by feeding
mode: carnivorous vs.
herbivorous
From Halver (page 7)
Focus: Gross Energy
Energy content of a substance (i.e., food) is
typically determined by completely
oxidizing (burning) the compound to carbon
dioxide, water and other gases
 the amount of energy given off is measured
and known as gross energy
 gross energy (GE) is measured by a device
known as a bomb calorimeter
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Gross Energy of
Feedstuffs
Gross Energy of Feedstuffs
Fats (triglycerides) have about twice the
GE as carbohydrates
 this is because of the relative amounts of
oxygen, hydrogen and carbon in the
compounds
 energy is derived from the heat of
combustion of these elements: C= 8 kcal/g,
H= 34.5, etc.
 typical heat from combustion of fat is 9.45
kcal/g, protein is 5.45, COH is 3.75
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Available Energy
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Gross energy only represents the energy present
in dry matter (DM)
it is not a measurement of its energy value to the
consuming animal!!
the difference between gross energy and energy
available to the animal varies greatly for different
foodstuffs
the key factor to know is how digestible the food
item is
digestible energy also varies by species
Digestible Energy
The amount of energy available to an animal
from a feedstuff is known as its digestible
energy (DE)
 REM: DE is defined as the difference between
the gross energy of the feed item consumed
(IE) and the energy lost in the feces (FE)
 two methods of determination: direct or
indirect
 by the direct method, all feed items consumed
and feces excreted are measured
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Digestible Energy
The indirect method involves only
collecting a sample of the feed and feces
 digestion coefficients are calculated on the
basis of ratios of energy to indicator in the
feed and feces
 indicator?: an inert indigestible compound
added to the feed
 indicators: natural (fiber, ash) or
synthetic (chromic oxide)
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DE Calculations
Direct Method
Feed energy - Fecal energy
% DE =
X 100
Feed energy
Indirect Method
% DE = 100 -
Feed energy
Fecal energy
X
Fecal indicator
Feed indicator
x100
Metabolizable Energy
Even more detailed!
 Represents DE minus energy lost from the
body through gill and urinary wastes
 More difficult to determine! Why?
 REM: all urinary wastes in water!!! How do you
collect that????
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Intake energy - (E lost in feces, urine, gills)
%ME = -------------------------------------- x 100
Feed energy
Metabolizable Energy
Use of ME vs DE would allow for a much more
absolute evaluation of the dietary energy
metabolized by tissues
 however, ME offers little advantage over DE
because most energy is used for digestion in
fish
 energy losses in fish through urine and gills
does not vary much by feedstuff
 fecal energy loss is more important
 forcing a fish to eat involuntarily is not a good
representation of actual energy processes
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Energy Ratios for
Rainbow Trout
Energy Balance in Fish
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Energy flow in fish is similar to that in mammals and
birds
fish are more efficient in energy use
energy losses in urine and gill excretions are lower in
fish because 85% of nitrogenous waste is excreted as
ammonia (vs. urea in mammals and uric acid in birds)
heat increment (increase) as a result of ingesting feed
is 3-5% ME in fish vs. 30% in mammals
maintenance energy requirements are lower because
they don’t regulate body temp
they use less energy to maintain position
Terrestrials vs. Aquatics
This section concerns the requirements for energy
by aquatic animals, how energy is partitioned, what
it is used for and how it is measured
 a major difference in nutrition between fish and
farm animals is the amount of energy required for
protein synthesis
 protein synthesis refers to the building of proteins
for tissue replacement, cell structure, enzymes,
hormones, etc.
 fish/shrimp have a lower dietary energy
requirement
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Factors Affecting Energy
Partitioning
Factors either affect basal metabolic rate
(e.g., body size) or affect other changes
 those affecting BMR are the following:
body size:non-linear, y = axb, for most
physiological variables, b values usually
range between 0.7 and 0.8
oxygen availability: have conformers
(linear) and non-conformers (constant until
stressed)
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O2 Consumption, by Size
(Fig. 2.1 from De Silva and Anderson)
Factors Affecting Energy
Partitioning
 temperature: most aquaculture species are
poikilotherms, significant effect, acclimation
required, aquaculture situation may mean rapid
temp changes
osmoregulation: changes in salinity result in
increased cost of energy
 stress: increased BMR resulting from heightened
levels of waste, low oxygen, crowding, handling,
pollution, etc. (manifested by hypoglycemia)
 cycling: various animal processes are cyclic in
nature (e.g., reproduction, migration)
Factors Affecting Energy
Partitioning
Those factors not affecting BMR are:
 gonadal growth: most energy diverted
from muscle growth into oogenesis,
deposition of lipid, can represent 30-40%
of body weight, implications????
 locomotion: major part of energy
consumption, varies due to body shape,
behavior and size, aquatic vs. terrestrial
issues
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Another Index: Gross
Conversion Efficiency (K)
Referred to as “K”, often used as an indicator
of the bioenergetic physiology of fish under
various conditions
 does not refer to an energy “budget”
 measures growth rate (SGR) relative to feed
intake over similar time periods
 both factors are related to body size:
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K = (SGR/RFI) x 100
SGR = (ln Wtf-lnWti)/(Tf - Ti) x 100
 RFI = (feed intake)/((0.5)(Wtf -Wti)(Tf-Ti))
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Energy and Growth
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Dietary excesses or deficiencies of useful energy can
reduce growth rate
this is because energy must be used for maintenance and
voluntary activity before it is used for growth
dietary protein will be used for energy when the diet is
deficient in energy relative to protein
when the diet contains excessive energy, feed intake is
typically reduced...fish don’t want to be fat????
this also reduces intake of protein and other nutrients
needed for growth
Dietary Sources of Energy:
proteins
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Considerable interaction between major nutrient groups
as energy sources
protein can be used as an energy source
not typically used because of cost and use for protein
synthesis (growth)
optimal ratio of protein:energy is around 22 mg PRO/kJ
(45 kJ/g PRO; old info)
species variation: 17 (59) for tilapia, 29 (35)for catfish,
29 (34) for mutton snapper (Watanabe, et al., 2001);
digestibility variation
temperature variation
Energy and Growth
Consumption of diets with low protein to energy
ratios can lead to fat deposition (fatty acid
synthetase)
 this is undesirable in food fish because it
reduces the dress-out yield and shortens shelf
life
 undesirable in shrimp due to build-up in hepatopancreas (midgut), ultimately affecting cooking
 low protein:energy diets can be useful for
maturation animals, hatchery animals raised for
release
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Energy Requirments of Fish
Determining the energy requirement of fish
has been a difficult task, slow in coming
 most research has been devoted to
identifying protein requirements, major
minerals and vitamins
 in the past, feeds were formulated letting
energy values “float”
 excess or deficiency of nutritional energy
does not often lead to poor health
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Energy Requirements of Fish
Further, if feeds are formulated with practical
feedstuffs (ingredients), their energy levels are
not likely to be off
 it is really a matter of cost: protein is the most
expensive component of the diet, COH sources
are cheap, why use protein as an energy
source????
 In terrestrials, feed is consumed to meet energy
requirements
 thus, as energy level of the feed goes up, protein
level is also designed to go up
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Energy Requirements of Fish
This is because terrestrial animals are typically
fed on an ad libitum basis
 fish, on the other hand, aren’t fed this way
 they are fed on a feed allowance basis (we
estimate feed fed)
 various studies have shown that the digestible
energy (DE) requirement for channel catfish and
carp was around 8.3-9.7 kcal DE/100 g fish/day
 in terms of age, dietary level of DE and protein
typically drop with age
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Protein, DE Requirements
of Channel Catfish, by Age
From Lovell, 1989
Energy Requirements of Fish
DE and protein requirements typically follow each
other, so the DE:P ratio (kcal/g) is fairly similar
with age (if anything, a small increase)
 this is partially due to the fact that fish grow
faster when young (higher tissue turnover rate,
demand for protein)
 however, the influence of energy is stronger than
that of protein relative to growth (Cuzon and
Guillaume, 1997)
 energy levels in crustacean diets usually range
similar to those of fish
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Energy Requirements of
Aquatics
The objective in formulating diets for most aquatic
species is the same: finding a cheap energy source
that is digestible and will spare protein
 glucose is not acceptable in that it causes high
blood sugar levels, poor growth, poor survival
 complex dietary COH’s prove better
 COH typically spares protein for growth
 increase in dietary energy tends to increase
performance when a diet low in protein is fed
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Energy Problems
Lipids and carbohydrates are typical
energy sources for crustaceans
 unfortunately, crustaceans are unable to
tolerate diets having greater than 10%
lipid (also hard to manufacture the feed!)
 this means that the major energy source
must be derived from COH
 various COH are used to various degrees
by crustaceans, making it difficult to
calculate the true energy value of diets
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